Pelli-Levi Dual Acuity Chart

Dual Acuity Chart 1a. Click to enlarge.

We designed this chart to be a quick diagnostic test for amblyopia. It is available here, free. Charts 1a and b have different random letter sequences. Both charts are provided as high resolution JPEG images that you may print at any size you like. The test is scale invariant, and may be administered at any test distance. We expect it to be insensitive to typical variations in printing contrast.

Chart 1a appears in Pelli, Levi, and Chung (2004), along with a theoretical explanation and the empirical work that led to the idea. Chart 1b is the same, but has a different letter sequence.

INSTRUCTIONS: Ask the observer to read all six letters on each row, continuing down the chart until the observer gets all three no-noise letters wrong. Give partial credit for each letter right in the last triplet in which any letters were correctly read. The chart is scale-invariant and may be used at any test distance. The score of interest is the difference in lines between the two sides. So far, we found no difference in six normals and a 1 or 2 line difference in the five amblyopes tested.